Clean optical path

 Stand up the instrument with the field lens end down. Unbolt the etalon/collimator section from the extension section. The collimator protrudes out the bottom, so flip the section over and set it on the table with the collimator up (Figure 3). Put the lens cover on the collimator to protect it while you perform the next step.

  

Figure 3: The etalon/collimator and extension sections of the Palomar Fabry-Perot instrument.

At this stage, it is recommended that you blow the dust off the inside of the field lens. However, if you are short on time, this step may be omitted. If time permits, unbolt the extension section from the field lens section. The diffuse flap, which is very fragile, protrudes out the bottom, so flip the extension section over and set it on the table with the flap up. Using the dry nitrogen, blow off the inner side of the field lens. Then reattach the extension section to the field lens section. Note that you may not need to remove the extension section at all if you can reach the field lens sufficiently to clean it with the section attached.

Next, confirm that the diffuse flap is rotated out of the optical path. The flap can rotate into the optical path for internal calibrations, but the flap and internal lamps are currently not used at Palomar Observatory. Next remove the lens cover from the collimator and blow off the inner surface of the collimator. If the collimator has an aperture adjustment (which the usual 306 mm one does not), confirm that the collimator lens is wide open. Reattach the etalon/collimator section to the extension section.